Disaggregation of Asphaltene Aggregates in Solutions Depending upon Affinity Indices of the Hansen Solubility Parameter Using Ultrasmall‑, Small‑, and Wide-Angle X‑ray Scattering

Disaggregation of asphaltene aggregate in solution is investigated using ultrasmall-, small-, and wide-angle scattering of X-rays up to 300 °C under isobaric conditions. Wide-angle scattering profiles indicate that the longer range structure of asphaltene aggregates in toluene collapses around 150 °C. A further increase in the temperature to 300 °C, however, leads to a slight reversion to the aggregated state. This specific behavior in solution is discussed in terms of the transition of asphaltene from a solid to a melted state around 200 °C and the corresponding change in affinity indices of the Hansen solubility parameter (HSP) at elevated temperatures. Ultrasmall- and small-angle scattering profiles of samples in solution clearly show the correlation of asphaltene aggregation with the HSP indices. To understand a deeper insight into key aspects of asphaltene aggregation behavior, small-angle scattering of model compounds in toluene is measured. The scattering intensities of model compounds are classified into two groups: suggesting and confirming molecular structures contributing to enhanced aggregation and heteroaromatics containing sulfur, peri-condensed aromatic rings, and porphyrin.